The present invention relates to semiconductor packages, and more particularly, to a cavity-down ball grid array (CDBGA) semiconductor package with a heat spreader.
A ball grid array (BGA) semiconductor package adopts advanced packaging technology, characterized in the use of a substrate with at least a semiconductor chip being mounted on a surface thereof and a plurality of array-arranged solder balls being implanted on an opposing surface of the substrate, so as to allow more input/output (I/O) connections (e.g. solder balls) to be implanted on a chip carrier (e.g. substrate) in response to high integration of the chip, to thereby electrically connect the semiconductor package to an external printed circuit board (PCB) by means of the solder balls.
U.S. Pat. No. 5,545,923 discloses a semiconductor package with a ground ring, a power ring and a plurality of signal fingers being formed on a substrate. As shown in FIG. 1a, in this semiconductor package 1, the ground ring 113, power ring 114 and signal fingers 115 are disposed at area other than a chip attach region 110 on a first surface 111 of the substrate 11. A semiconductor chip 12 having a plurality of ground pads, power pads and signal pads (not shown) is mounted on the chip attach region 110. A wire-bonding process is performed to form a plurality of ground wires 133, power wires 134 and signal wires 135, wherein the ground wires 133 electrically connect the ground pads of the semiconductor chip 12 to the ground ring 13 of the substrate 11, the power wires 134 electrically connect the power pads of the semiconductor chip 12 to the power ring 114 of the substrate 11, and the signal wires 135 electrically connect the signal pads of the semiconductor chip 12 to the signal fingers 115 of the substrate 11. Then, a plurality of solder balls 14 are implanted on a second surface 112 of the substrate 11, and electrically connected to the corresponding ground ring 113, power ring 114 and signal fingers 115 respectively via conductive traces (not shown) formed on the second surface 112 of the substrate 11. By electrically connecting the semiconductor package 1 to an external device via the solder balls 14, the ground ring 113 and power ring 114 help maintain electrical quality of the semiconductor package 1, and provide grounding effect and power supply as required for operation of the semiconductor chip 12.
However, due to dense arrangement of electronic elements and circuits on the highly integrated semiconductor chip, a large amount of heat is produced during operation; if the heat can not be effectively dissipated, it would seriously damage performance and lifetime of the semiconductor chip. Moreover, this package structure lacks sufficient shielding effect, and thereby is easily subject to external electromagnetic and noise interference.
In order to solve the foregoing problems, U.S. Pat. No. 6,020,637 discloses a cavity-down ball grid array (CDBGA) semiconductor package; as shown in FIG. 1b, this semiconductor package 2 comprises: a tape substrate 22, a heat spreader 200, a ground plane 202, at least a semiconductor chip 23, a plurality of bonding wires 24, an encapsulant 25 and a ball grid array 260.
The above semiconductor package 2 utilizes a two-layer heat sink 20 composed of the heat spreader 200, an adhesive layer 201 and the ground plane 202, wherein the ground plane 202 is formed with an opening 2020 for chip accommodation, and a ground ring 21 is disposed around the opening 2020. The substrate 22 is attached to the ground plane 202, and formed with a plurality of vias 220. The semiconductor chip 23 is mounted to the heat spreader 200 by means of the adhesive layer 201 and received within the opening 2020; this semiconductor chip 23 is electrically connected to the ground ring 21 by a plurality of first bonding wires 240a, and electrically connected to conductive traces (not shown) formed on the substrate 22 by a plurality of second bonding wires 240b, allowing the semiconductor chip 23 and bonding wires 240a, 240b to be encapsulated by the encapsulant 25. And, a plurality of solder balls 260a, 260b are implanted on the substrate 22, wherein the solder balls 260a are connected to the vias 220 of the substrate 22 for allowing the heat sink 20 to be electrically connected to a printed circuit board (PCB, not shown) by the vias 220 and solder balls 260a (ground balls).
Although the above semiconductor package 2 provides solutions to the problems of heat dissipation and electromagnetic interference, it requires complex fabrication processes and high costs; further, voids may be easily formed in the vias 220 during fabrication, thereby degrading electrical connection between the ground balls 260a and the ground plane 202.
Furthermore, the ground ring 21 of the ground plane 202 used in the above semiconductor package 2 is also made by complex processes. First, the ground ring 21 is formed by plating gold (Au) or silver (Ag) over the ground plane 202; then, a black oxidation process is performed at area other than the ground ring 21 on the ground plane 202, allowing the ground plane 202 to have good adhesion to the tape substrate 22. However, the black oxidation process would easily contaminate the pre-formed ground ring 21, and thus degrade bondability of the first bonding wires 240a and adherence between the ground ring 21 and the encapsulant 25, thereby adversely affecting quality and reliability of fabricated products.
Therefore, the problem to be solved herein is to provide a semiconductor package, which can simplify fabrication processes, reduce costs, and solve the problems of heat dissipation, electromagnetic interference and crosstalk effect.
A primary objective of the present invention is to provide a cavity-down ball grid array (CDBGA) semiconductor package with a heat spreader, wherein a substrate is mounted in a cavity of the heat spreader, and an electrically conductive adhesive is applied between an inner wall of the cavity and edges of the substrate, whereby the heat spreader can be electrically connected to a metal ground layer exposed to the edges of the substrate by means of the electrically conductive adhesive, so as to simplify fabrication processes, reduce costs, and solve problems of heat dissipation, electromagnetic interference and crosstalk effect.
In accordance with the above and other objectives, the present invention proposes a CDBGA semiconductor package with a heat spreader, comprising: a substrate having a first surface and a second surface, and formed with an opening, a metal ground layer exposed to edges of the substrate, at least a ground ring formed at peripheral area on the second surface of the substrate, and a plurality of ground vias; a heat spreader formed with at least a cavity, allowing the substrate to be mounted in the cavity with the first surface of the substrate being attached to the heat spreader; a semiconductor chip having a circuit surface and a non-circuit surface, and mounted in the opening of the substrate with the non-circuit surface of the semiconductor chip being attached to the heat spreader; an electrically conductive adhesive for connecting the exposed metal ground layer and the ground ring of the substrate to an inner wall of the cavity of the heat spreader, allowing the ground layer and ground ring to be electrically coupled to the heat spreader by the electrically conductive adhesive; a plurality of bonding wires for electrically connecting the semiconductor chip to the substrate; an encapsulant for encapsulating the semiconductor chip and bonding wires; and a plurality of solder balls implanted on the second surface of the substrate, for electrically connecting the semiconductor chip to an external device
The above CDBGA semiconductor package according to the invention is characterized in the use of the electrically conductive adhesive being applied between edges of the substrate and the cavity of the heat spreader, so as to allow the exposed ground layer and the ground ring to be electrically coupled to the heat spreader via the electrically conductive adhesive. As a result, by simplified processes and lower costs for fabricating the semiconductor package, the heat spreader can be included in a grounding circuit path of the semiconductor chip, and heat produced from the semiconductor chip can be effectively dissipated via the heat spreader. This thereby prevents floating ground effect and excess grounding resistance, and solves problems of heat dissipation, electromagnetic interference and crosstalk effect.